Electric power utilities in the US and around the world are currently in the process of upgrading their distribution systems to simplify and automate system operation by implementing enhanced monitoring, distribution automation and control solutions. The ultimate goal from a distribution system operations standpoint, as stated by many utilities in their roadmaps to the so-called Smart Grid, is to achieve smart, self-healing grids. These grids should be capable of automatic isolation of permanent faults and automatic system reconfiguration, to quickly restore power to as many customers as possible by switching affected customers over to alternative sources of power in the event of an interruption.
This goal can be achieved within the distribution management system (DMS) framework by adding various smart sensors, integrating sensor and meter data into decision making process, and using advanced hybrid (wired/wireless) communications infrastructure, to implement automatic fault location, isolation and load restoration schemes. However, this flexibility introduces some new problems in systems operation. In particular, automatic network reconfiguration may result in situations where Intelligent Electronic Devices (IEDs) such as substation relays and field reclosers that have been pre-configured to protect the system from abnormal conditions may no longer provide selective operation, i.e., operation that ensures that only those fault protection devices closest to a fault are triggered. In a new configuration created by an automatic recovery system, these devices may fail to operate during faults, or can mis-operate and create nuisance trips during normal operation conditions. Accordingly, improved techniques for fault protection coordination are needed.